predators, and these behaviors feed back on the predators.
Rodents have provided and will continue to provide a cru-
cible for formulating and testing theories of the nonlethal
effects of predators.
Summary
The ecology of fear examines the behavioral, population,
and community consequences of the nonlethal effects of
predators. Predation risk may reduce activity levels, shift
activity from risky to safe places, alter mating behaviors
and reproduction, increase levels of vigilance and appre-
hension, and alter intra- and interspecific competitive inter-
actions. Furthermore, fear in response to predation risk
may alter life-history characteristics such as growth rates,
dispersal, and age at maturity. These fear responses are
adaptations that serve to maximize the prey’s fitness in the
face of predation risk. In this chapter, our aim was to ex-
amine fear and its effects on the foraging, breeding, and so-
cial behavior of rodents. We refer mostly to boreal voles
(Microtusand Clethrionomys) living under relatively dense
vegetation and to desert rodents (e.g., Gerbillus) exposed
to predation in more open environments. All of these ro-
dents share risks from terrestrial predators (mammals and
snakes) and avian predators (raptors and owls). Different
predators pose different challenges and may present differ-
ent cues to their rodent prey. Predation risk is a cost-benefit
assessment of foraging, breeding, and social interactions
such as territoriality, interference competition, and group
vigilance. The costs of predation may have implications for
foraging in terms of space use, habitat selection, and timing
and /or suppression of breeding; social foraging in terms of
vigilance, alarm calls, and various forms of safety in num-340 Chapter Twenty-Eight
Table 28.1 Comparing and contrasting the life-history properties of boreal voles and desert gerbils relevant to their predators
and to the rodents’ responses to the risk of predation
Boreal voles Desert gerbilsDiet Lower quality: herbs and grasses Higher quality: seeds
Reproductive ecology Larger litters; shorter gestation time; shorter weaning period Smaller litter; longer gestation time; longer weaning period
Activity time Polyphasic: Longer activity time; roughly 2 hours of activity Nocturnal: Short activity time; highest activity early in the
followed by 2 hours of rest. night.
Food storage Noncaching Extensive caching
Burrows Susceptible to predation. Relatively immune to predation; snakes may sit and wait at
burrow entrances.
Specialist predators Weasel and stoat Probably none?
Generalist predators Fox, hawks, owls Fox, owls, shrikes, monitor lizard, snakes
Metabolism High mass-specific metabolic rate (may be adaptation to high Low mass specific metabolic rate (may be antipredator
activity times) adaptation by lowering time spent active).
Direct cues of predation risk Predator odor, weasel, owls?, hawks? Owls, foxes, snakes; likely respond to sound and visual
spotting of predators; predator odors?
Indirect cues Microhabitat: cover safer than open; moonlight? Microhabitat: Cover generally safer than open; moonlight
avoidance
Population dynamics Multiannual fluctuations or cycles with large amplitudes; Seasonal fluctuations in response to pulse of seed from
likely due to time lags in prey and specialist-predator dynamics. spring bloom; year to year fluctuations likely due to year
to year variability in rainfall amounts and patterns.
Exposure to predation Per-unit activity risk is likely lower, but daily exposure to risk is Per-unit activity risk is high, but mitigated by low activity
likely higher. times biased toward particularly profitable periods;
lower daily exposure to risk.
Behavioral flexiblity Need to forage frequently and inability to cache likely reduces Ability to cache increases greatly the latitude for anti-
latitude for antipredator behaviors. predator behaviors, either through apprehension while
foraging or time allocation to safer places and times.
Fear system Population size driven (N-driven): the population response to Fear driven (m-driven): the population response to risk is
risk is to have high feeding rates and high fecundity rates to forgo fecundity by forgoing feeding during risky times
to compensate for high predation rates. In effect, voles pay or risky places. In effect, gerbils pay the cost of predation
their cost of predation by feeding the predators. by not feeding the predators through apprehensive
foraging and lower fecundity.
NOTES: Although there should be much generality with respect to comparing boreal rodents with desert rodents in general, the specific systems from which these conclusions
are drawn emerge mostly from studies in Fennoscandia on Microtus agrestisand Clethrionomys glareolus,and studies in the Negev Desert with Gerbillus pyramidumand
G. andersoni.